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Determination of acrylonitrile in air application of thermal desorption instrument

2020-07-27 09:06:19 Practical thermal analysis thirty-five

principle

Acrylonitrile in the air was collected in a silica gel sampling tube at room temperature. After thermal desorption, it was separated by GDX-102 column and detected by flame ionization detector. The retention time was used for qualitative analysis and peak height quantification.

  

instrument

Silica gel sampling tube: a glass tube with a length of 15cm, an inner diameter of 3.5-4.0mm and an outer diameter of about 6mm. It contains 200mg of silica gel with 40-60 mesh. Both ends are fixed with glass wool and sealed with plastic caps. This tube can be used in a short time.

Sampling pump, 0 ~ 1L / min.

Syringe, 100ml, 1ml.

Micro syringe, 1 pl.

Thermal desorption unit Domestic thermal desorption It is mainly composed of heater, temperature controller, thermometer and gas flow controller. The temperature control range is 100 ~ 350 ℃, the desorption gas is nitrogen, and the flow control range is 50 ~ 100ml / min. The structure of the thermal desorption device used shall be such that the silicone tube can be easily inserted into the heater, and the gas passing through the pipe shall be preheated first, and the silica gel shall be heated evenly.

The signal-to-noise ratio of 7 ng acrylonitrile is not less than 3:1

Chromatographic column: column length 2m, inner diameter 4mm, stainless steel column, packed with GDX-102 stationary phase.

Column temperature: 150 ℃

Detection room temperature: 170 ℃

Temperature of vaporizer: 170 ℃;

Carrier gas (nitrogen): 110ml / min.


Sampling

Remove the plastic caps at both ends of the sampling tube at the sampling site, place them vertically, and collect 1L air at the speed of 0.1l/min. After sampling, put on the plastic cap and take it back to the laboratory for analysis.


Analysis steps

Controlled trial

Sample treatment

The silica gel tube (3.1) without sample was used as blank control according to the sample treatment (6.2) steps.  

Remove the plastic caps at both ends of the sample tube, connect it with a 100ml syringe, put it on the thermal desorption device, and use nitrogen to desorb to 100ml at the speed of 100ml / min at 180 ℃.

   

Drawing of standard curve

Take a certain amount of acrylonitrile (0.8060mg at 20 ℃) with a 1pl micro syringe, inject it into a 100ml syringe, dilute it to a certain volume with clean air, take a certain amount of the above gas and dilute it with air to 0.05, 0.10, 0.15, 0.20, 0.25pg/ml acrylonitrile standard gas. Take 1ml sample respectively, measure the retention time and peak height, repeat three times for each concentration, take the average value of peak height, plot the peak height with acrylonitrile content, and draw the standard curve. Retention time is a qualitative indicator.


Determination

Take 1ml desorbed gas for injection, qualitative analysis with retention time and quantitative analysis by peak height.

 Solid thermal desorption